I wanted to make sure everything was hooked up properly, so I swapped pins (dumb and possibly expensive diagnostic) to make sure everything was connected as it should.

Car wouldn't start, or oil level light illuminated when the pins were placed improperly. So at least I know I built the harness correctly.

The interesting thing is that the pressure gauge would be pegging even if disconnected from the connector, as long as the oil level sender was connected. Do these two share a common connection or switch somewhere?